Solving for a Variable in Formulas - Pre Algebra

1. Solve $d = rt$ for $t$.

   $t = \frac{d}{r}$. Divide both sides by $r$.

2. Use $P = 2l + 2w$ to find $w$ when $P = 30$ and $l = 9$.

   $w = 6$. $30 = 18 + 2w$, so $2w = 12$.

3. Use $A = lw$ to find $l$ when $A = 48$ and $w = 6$.

   $l = 8$. Divide both sides by 6.

4. Solve $P = 2l + 2w$ for $l$.

   $l = \frac{P - 2w}{2}$. Subtract $2w$, then divide by 2.

5. Solve $A = lw$ for $w$.

   $w = \frac{A}{l}$. Divide both sides by $l$.

6. Use $I = Prt$ to find $t$ when $I = 60$, $P = 500$ and $r = 0.04$.

   $t = 3$. $Pr = 20$, so $60 = 20t$.

7. Use $F = \frac{9}{5}C + 32$ to find $C$ when $F = 212$.

   $C = 100$. $\frac{9}{5}C = 180$, so $C = 180 \cdot \frac{5}{9} = 100$.

8. Use $A = \frac{1}{2}bh$ to find $h$ when $A = 24$ and $b = 6$.

   $h = 8$. $24 = 3h$, so $h = 8$.

9. Solve $y = mx + b$ for $b$.

   $b = y - mx$. Subtract $mx$ from both sides.

10. Use $V = lwh$ to find $h$ when $V = 120$, $l = 5$ and $w = 4$.

    $h = 6$. $120 = 20h$, so $h = 6$.

11. Use $d = rt$ to find $t$ when $d = 150$ and $r = 50$.

    $t = 3$. Divide both sides by 50: $150 \div 50 = 3$.

12. Solve $C = 2\pi r$ for $r$.

    $r = \frac{C}{2\pi}$. Divide both sides by $2\pi$.

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